1. Field of the Invention
The present disclosure relates to display technical field, and in particular, to a backlight unit of high light coupling efficiency.
2. The Related Arts
As a development of liquid crystal televisions (TVs) is tended to large size and high-definition 4K even 8K resolution technique, the number of pixel units of a liquid crystal display (LCD) panel is increased, the size and the aperture ratio of a pixel are decreased, and the transmittance of a LCD panel is also reduced.
In order to improve transmittance of a large-sized LCD panel, it needs to enhance backlight brightness. As for an edge type LCD panel, if it merely adopts unilateral incident light, it cannot get rid of limits of flow brightness of a single lamp and poor heat dissipation effect of a conventional Light-Emitting Diode (LED). Plus, transmittance of a large-sized high definition LCD panel is relatively low, thus, a designed brightness of a single long side cannot achieve a set brightness. Thus, there is a method for enhancing a backlight brightness in the prior art. In specific, both short and long sides of a light guide plate are provided with edge type light sources simultaneously. However, the light guide plate having this structure cannot dissipate heat uniformly, which is easily heated and expanded due to moisture absorption to cause mura (i.e., various shadow phenomenon caused by nonuniform brightness of a display). Meanwhile, expansion of the light guide plate may also cause the LED to crack. In order to avoid those phenomena, designers generally reduce risks of occurrence of warping and hitting lamp by increasing a light coupling distance between the LED and the light guide plate. However, due to the increase of the light coupling distance, a light coupling efficiency of the light incident into the light guide plate is greatly decreased, especially, in the types of the devices that require for a narrow bezel design, in order to avoid edge light leakage, it is generally to add a material with low reflectivity over a light coupling region to reduce a risk of light leakage, so that the light coupling efficiency is further reduced.